Operation of reaction motors



United States atent Ofiice 3,357,185 Patented Dec. 12, 1967 3,357,185 OPERATION OF REACTION MOTORS Richard Alden Crooker, Denville, Andrew Fung Lum,

Dover, and Frank James Loprest, Chester, N.J., assiguors to Thiokol Chemical Corporation, Bristol, Pa. No Drawing. Filed Feb. 20, 1%3, Ser. No. 260,947

I 5 Claims. (Cl. 60-214) and an oxidant, e.g., liquid oxygen. These high temperature gases, emerging from the exhaust nozzle at high velocities, provide the thrust to propel the rocket. Some propellant systems, useful in rocket motors, require an igniting means to initiate combustion. Other propellant systems, however, ignite spontaneously upon contact between'the fuel and oxidizer and are called hypergolic propellants.

A typical example of a spontaneously ignitable propellant system is the pentaborane-hydrazine combination.

This combination is extremely attractive as a rocket propellant system by virtue of its high specific impulse and its relatively low flame temperature. However, difliculty has heretofore been experienced in obtaining reliable spontaneous ignition of the pentaborane-hydrazine propellant system. It is most desirable that ignition take place immediately upon the contacting of the propellant components in the combustion ZOne. Otherwise, an excessive quantity of the propellant will accumulate in the combustion zone before ignition occurs, producing a dangerous condition inviting explosive destruction of the rocket motor and injury to attendant personnel.

Various proposals have been made for obtaining reliable spontaneous ignition of the pentaborane-hydrazine propellant system. One such proposal has been the use of an additional propellant, such as nitrogen tetroxide, N 0 flowing from its own tank, to aid the initial combustion. This procedure, however, requires the addition of complex equipment, and therefore tends to decrease the operational reliability of the reaction motor system.

It is accordingly an object of this invention to provide an improved method of operating liquid propellant reaction motors. Another object of the invention is to provide an improved method of reducing the ignition delay of a hypergolic propellant system in a rocket motor. Another object of the invention is to provide propellant compositions which render the hydrazinepentaborane reaction system reliably hypergolic. It is a further object of the invention to avoid the formation of undesirable combustion products. Other objects and advantages of the invention are in part obvious and in part pointed out hereinafter.

Applicants have found that the addition of an alkylated hydrazine, such as a lower alkyl hydrazine, to the pentaborane-hydrazine propellant system, makes the said system reliably hypergolic when the pentaborane and hydrazine components are brought together in the combustion chamber of a rocket motor. Most suitable of these alkyl hydrazines are unsymmetrical dimethylhydrazine, monomethyl hydrazine, ethyl hydrazine, and propyl hydrazine.

The amount of the alkylated hydrazine additive suitably added to the pentaborane-hydrazine propellant system will usually be in the range of 0.1 to 10 weight percent, and preferably in the range of 2.5 to 10 weight percent, based on the mixture of the hydrazine and hydrazine additive. Amounts of said additive as low as 0.1%

by weight are useful and quantities far in excess of 10% are operative, but are usually not economically attractive in attaining the objects of the present invention.

When substituted hydrazine additives are used as disclosed herein, a certain amount of elemental carbon is produced in the oxygen-free environment of the combustion zone. It has been found that this carbon may be eliminated as carbon monoxide by dissolving stoichiometric quantities of an oxidizer in the hydrazine. For example, one mole of hydrazine diperchlorate of the formula N H (CIO will theoretically convert eight moles of carbon to carbon monoxide. However, from a practical viewpoint, amounts of oxidizer up to 10% in excess of that theoretically required are necessary for optimum carbon removal. The use of soluble oxidizers such as hydrazine perchlorates and hydrazine nitrates prevents carbon fouling of the reaction motor and provides more eificient and complete utilization of the components of the propellant system. In general the oxidizer is desirably used to the extent of 1% to 10% by weight based on the total weight of hydrazine and alkyl hydrazine employed. The presence or absence of the oxygencontaining compounds does not affect the hypergolicity of this propellant system, but these additives are helpful when the formation of elemental carbon is undesirable.

In order to point out more fully the nature of the present invention, the following specific examples are given of compositions embodying the invention and the results attainable when the compositions are used according to the process of the invention. In the examples, pentaborane stabilized against air reactivity for ease of experimental handling with 2% by weight of iodine was brought into contact with hydrazine and various hydrazine-containing compositions, and the rapidity of ignition was observed. As indicated in the examples, when none of the beneficial additives herein disclosed are incorporated into the hydrazine no ignition takes place, or if ignition does take place, it does so only after a considerable period of time, and usually after at least ten minutes. However, the addition of alkyl hydrazine compounds provides a method whereby such delay in ignition is avoided.

Example 1 A mixture containing by weight 2.7% hydrazine nitrate, 2.5% unsymmetrical dimethyl hydrazine, and 94.8% of hydrazine was prepared. Four parts by volume of this mixture were placed in a reaction vessel and one part by volume of pentaborane, containing 2% by weight of iodine inhibitor, was injected into the hydrazine composition at a temperature of F. A spontaneous ignition occurred in less than one second after the addition of the hydrazine component. Multiple runs confirmed the fact that the rapid ignition of this mixture is reproducible.

Example 2 A mixture containing 10% by weight of unsymmetrical dimethyl hydrazine and hydrazine was prepared. Four parts by volume of this mixture were placed in a reaction vessel, then one part by volume of pentaborane, containing 2% by weight of iodine inhibitor, was injected into the hydrazine composition. A spontaneous ignition occurred within one second after the addition of the hydrazine component. This procedure was repeated several times with a rapid spontaneous ignition occurring each time.

When, in additional testing, the amount of usymme-trical dimethyl hydrazine additive in the hydrazine composition was reduced to 5% and to 3% respectively, spontaneous ignition still took place immediately upon the contact of the hydrazine composition and the pentaborane.

Example 3 A mixture containing 10% by weight of monomethyl hydrazine and 90% by weight of hydrazine was prepared. Four parts by volume of this mixture were placed in a reaction vessel, and one part by volume of pentaborane, containing 2% by weight of iodine inhibitor, was injected into the hydrazine composition. A spontaneous ignition occured in less than one second.

This run was repeated three times with an immediate and spontaneous ignition occurring each time.

From the foregoing examples, it should be apparent that the present invention provides an eifective method of rendering the pentaborane-hydrazine propellent system more reliably hypergolic. By incorporating, in the normal hydrazine, from 0.1% to of lower alkyl-substituted hydrazine, the probability of prompt spontaneous ignition of the system can be substantially increased. It is of course to be understood that the foregoing examples are intended to be illustrative, and that numerous changes can be made in the ingredients, proportions and conditions set forth therein, without departing from the spirit of the invention as defined in the appended claims.

We claim:

-1. A composition adapted to be used with pentaborane as the propellant system of a liquid bi-propellant reaction motor, said composition being essentially composed of a mixture of hydrazine, lower alkyl hydrazine and as an oxidant, a hydrazine salt compatible with said hydrazine components, said mixture containing 0.1% to 10% by weight of said lower alkyl hydrazine and a quantity of said oxidant sufficient to react with the carbon of said alkyl hydrazine to form carbon monoxide.

2. A composition as in claim 1 where said oxidant is hydrazine perchlorate. 1

3. A method of operating a liquid bipropellant reaction motor which comprises continuously and separately introducing into a combustion zone of said motor pentaborane and a mixture of hydrazine, lower alkyl hydrazine and as an oxidant, a hydrazine salt, said mixture containing 0.1% to 10% of said hydrazine salt suflicient to react with the carbon of said alkyl hydrazine to form carbon monoxide, and contacting said pentaborane and hydrazine mixture in said combustion zone to cause them to react to form a hot gas stream for driving said motor.

4. A method according to claim 3 and wherein said oxidant is hydrazine perchlorate which is present to the extent of 1% to 10% by weight of said mixture.

5. A method according to claim 3 and wherein said oxidant is hydrazine nitrate which is present to the extent of 1% to 10% by weight of said mixture.

References Cited UNITED STATES PATENTS 3/ 1963 Rose 149-36X 7/ 19-64 Tyson -354 OTHER REFERENCES 

3. A METHOD OF OPERATING A LIQUID BIPROPELLANT REACTION MOTOR WHICH COMPRISES CONTINUOUSLY AND SEPARATELY INTRODUCING INTO A COMBUSTION ZONE OF SAID MOTOR PENTABORANE AND A MIXTURE OF HYDRAZINE, LOWER ALKYL HYDRAZINE AND AS AN OXIDANT, A HYDRAZINE SALT, SAID MIXTURE CONTAINING 0.1% TO 10% OF SAID HYDRAZINE SALT SUFFICIENT TO REACT WITH THE CARBON OF SAIN ALKYL HYDRAZINE TO FORM CARBON MONOXIDE, AND CONTACTING SAID PENTABORANE AND HYDRAZINE MIXTURE IN SAID COMBUSTION ZONE TO CAUSE THEM TO REACT TO FORM A HOT GAS STREAM FOR DRIVING SAID MOTOR. 